Grouped bar-chart in Kibana using Vega-lite - elasticsearch

Question

From looking at https://vega.github.io/editor/#/examples/vega-lite/bar_grouped it shows example of creating grouped bar chart from a table of data.
In my case since I am getting data from elasticsearch it is not in tabular form.
I can't figure out a way to create two bar chart for each sum metric on a bucket.
"buckets" : [
{
"key_as_string" : "03/Dec/2019:00:00:00 +0900",
"key" : 1575298800000,
"doc_count" : 11187,
"deploy_agg" : {
"buckets" : {
"deploy_count" : {
"doc_count" : 43
}
}
},
"start_agg" : {
"buckets" : {
"start_count" : {
"doc_count" : 171
}
}
},
"sum_start_agg" : {
"value" : 171.0
},
"sum_deploy_agg" : {
"value" : 43.0
}
},..
I want to create two bars, one representing value of sum_start_agg and another one representing sum_deploy_agg value.
This is what I had for one bar chart.
"encoding": {
"x": {
"field": "key",
"type": "temporal",
"axis": {"title": "DATE"}
},
"y": {
"field": "deploy_agg.buckets.deploy_count.doc_count",
"type": "quantitative",
"axis": {"title": "deploy_count"}
}
"color": {"value": "green"}
"tooltip": [
{
"field": "deploy_agg.buckets.deploy_count.doc_count",
"type": "quantitative",
"title":"value"
}
]
}

Answer 1

You can use the Fold Transform to fold your two columns so that they can be referenced in an encoding. It might look something like this:
{
"data": {
"values": [
{
"key_as_string": "03/Dec/2019:00:00:00 +0900",
"key": 1575298800000,
"doc_count": 11187,
"deploy_agg": {"buckets": {"deploy_count": {"doc_count": 43}}},
"start_agg": {"buckets": {"start_count": {"doc_count": 171}}},
"sum_start_agg": {"value": 171},
"sum_deploy_agg": {"value": 43}
}
]
},
"transform": [
{
"fold": ["sum_start_agg.value", "sum_deploy_agg.value"],
"as": ["entry", "value"]
}
],
"mark": "bar",
"encoding": {
"x": {"field": "entry", "type": "nominal", "axis": null},
"y": {"field": "value", "type": "quantitative"},
"column": {"field": "key", "type": "temporal"},
"color": {"field": "entry", "type": "nominal"}
}
}